The alkaline battery comprises an alkaline aqueous solution, such as a potassium hydroxide aqueous solution, as an electrolyte and also comprises a positive electrode and a negative electrode separated electrically from each other by a separator.
The negative electrode comprises negative electrode active materials, such as zinc, that generate electrons while being oxidized (oxidation reaction). The positive electrode comprises positive electrode active materials, such as manganese dioxide, which absorbs electrons via reduction reaction.
Thereby, in the alkaline battery, chemical energy generated in connection with oxidation-reduction reaction is taken out as electric energy.
Such an alkaline battery separator needs to meet various requirements. For instance, such a separator should: (1) prevent internal short-circuiting between the positive electrode and the negative electrode; (2) have satisfactory electrolyte absorption capacity to cause sufficient electrogenic reactions, while having good ionic conductivity as well as low electric resistance; (3) occupy a small space when incorporated into a battery so as to increase the amounts of positive and negative electrode active materials (and therefore increasing the battery life); and (4) withstand, after incorporated into a battery, buckling caused by impacts due to vibrations or accidental drops during transport or handling, which may lead to internal short-circuiting of the battery.
In recent years, the popularization of digital equipment requires novel alkaline batteries having further improved discharge performance. It is possible to enhance the discharge performance of a battery by using a thinner separator in order to increase an amount of active materials to be added, but such a thinner separator may facilitate short circuit caused by penetration of a metallic crystal. Moreover, larger amount of active materials to be added and others may increase in amount of metal impurities in the active materials. For example, metals, such as copper, contained in positive electrode active materials as well as in impurities of the positive electrode active materials may ionize so as to precipitate on the negative electrode side. The precipitated metals may become the cause of a short circuit.
In order to solve such a problem, Patent Document 1 (JP Laid-open Patent Publication No. 2007-507850) describes a battery including a separator having a trapping layer. As the trapping layer, there is described a solvent- and ion-permeable gel matrix which contains a trapping component (for example, metal) being capable of trapping a metal ion. According to this invention, even when the cathode active materials (for example, copper materials) are dissolved in electrolyte so as to generate Cu(OH)42− ions, the trapping layer can reduce and/or absorb these ions, resulting in impeding diffusion of the ions to the anode and generation of metal copper by consuming the zinc that is the anode active material.
Patent Document 2 (JP Laid-open Patent Publication No. 2008-21497) has proposed an alkaline battery comprising a chelating agent, such as EDTA, blended with a cathode mixture of an alkaline battery. According to this invention, the addition of a chelating agent to the cathode mixture can form complexes of copper ions even if the ions of copper, which is a heavy metal impurity contained in manganese dioxide in the cathode mixture, arc generated by ionization from the manganese dioxide.